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erice writes "Astronomers in Chile linked four telescopes together to form a single virtual mirror 130 meters in diameter. Previous efforts had linked two telescopes but this is the first time that all four had been linked. 'The process that links separate telescopes together is known as interferometry. In this mode, the VLT becomes the biggest ground-based optical telescope on earth. Besides creating a gigantic virtual mirror, interferometry also greatly improves the telescope's spatial resolution and zooming capabilities.'"

the big problem I think is atmospherics. Getting two scopes to sync is the easy bit, getting them to dance out shimmer is difficult - the idea of interferometry (FYI) is to separate two points - difficult to do if they're moving in different directions in two (or four) locations at the same time. I reckon the best they could do here is to apply some sort of real time or maybe even predictive correction to the raw data (wind sensors?). Job even harder if the sensors are located a continent or two apart...

The coolest thing I learned about the VLT is that it uses a laser to excite sodium particles 90km up in the atmosphere which creates a very faint 'star' at a very well-known distance. This reference point is used to make tiny adjustments to the mirrors to correct for atmospheric turbulence. These telescopes are not continents apart, they are all at the Paranal observatory in Chile. The light from each telescope is routed underground through equal-length tunnels to a central point to make one GIANT image. From wikipedia, "when all the telescopes are combined, the facility can achieve an angular resolution of about 0.001 arc-second. This is equivalent to roughly two metres at the distance of the Moon."

the big problem I think is atmospherics. Getting two scopes to sync is the easy bit, getting them to dance out shimmer is difficult - the idea of interferometry (FYI) is to separate two pointsEach telescope has its own adaptive optic correction system, which takes care of the atmospheric aberrations within its own field of view. The separate telescopes' corrected images are then combined interferometrically, plus and additional A-O step to account for atmospheric differences between telescopes. I'd call i

A-O is "real" adaptive optics: measure the wavefront error and move some physical object, e.g., deformable mirrror, to correct the phase errors. It takes a bunch of math, but depends on fixing the light before it becomes an image.

Since I don't know I'll ask...Can this scale up to multiple scopes, and does this need a minimum size scope ?

I'm asking for the following reason:I think it would be a great service to mankind if, people that own telescopes could hook up the telescopes every now and then to a central platform and let the computers observe the local solar system for possible unknown items in space. given, I think that I think the idea is years away, I would like to start tinkering with the idea....

it seems that the application for this is amazingly great for light year distances and beyond, I am just wondering if on the smaller scale ( with smaller telescopes ) would it work on a solar system scale.

If we could have well synchronized time (down to a small fraction of observed wave's period), and sensors that could heterodyne the incoming optical signal, then we could simply frequency-shift the optical signal, digitize the I and Q (preserves phase and amplitude), record it with the timestamps, and do interferometry completely offline. No adaptive optics needed, it'd be all done digitally. It's done that way for some radioastronomy and is no big deal, the only problems are technical when you think of doi

It is my understanding that by seperating the detectors over large distances in space or time, it makes it easier to detect and correct for atmospheric abberations. Which is one of the reasons interferometers were built in the first place.

I think Keck's got near-IR interfometry working. I very strongly suspect VLT is doing near-IR as well, but the article doesn't say. And this use of an optical chip instead of mirrors... dunno.

I'm still waiting for the "Ohana" project that's supposed to link Keck 1+2, Subaru, Gemini, and maybe some of the 3-meter-class scopes near them through single-mode fiber. Maximum baseline if they build that? 800 meters, if I recall.

Your referring to the Dawes's resolution limit [wikipedia.org] [arc sec] = 116 / Aperture Diameter [mm] (for green light), it's actually the edges that contribute the most to resolution, where the glass in the middle increases the light gathering ability more and the glass in the center usually doesn't do anything. As the glass gets bigger, the cost increases exponentially. The lack of light gathering is easy to compensate by increasing the exposure time.

I think what you're trying to point out is that the TFS is misleading, if the submitter intended to imply that interferometry improves both aperture and resolution. With interferometry, of course, one gets the resolution of the baseline (in this case 130m), but the aperture remains the same as the telescopes themselves. Meaning that one can improve the resolution of images, but not their sensitivity -- the light photons that fall onto the ground between the telescopes are still lost, whether or not interf

Well, I don't know, Mr. AC. To which "people" do you refer? Most "people" I know in astronomy define an "aperture" in the same way Wikipedia does [wikipedia.org]:

[T]he aperture stop is the stop that determines the ray cone angle, or equivalently the brightness, at an image point.

In some contexts, especially in photography and astronomy, aperture refers to the diameter of the aperture stop rather than the physical stop or the opening itself. For example, in a telescope the aperture stop is typically the edges of the objective lens or mirror (or of the mount that holds it). One then speaks of a telescope as having, for example, a 100 centimeter aperture. [emphasis added]

Most astronomers I know actually would, in fact, tell you that aperture masking turns a 10m aperture into a cm-range aperture, since the sensitivity of the resulting telescope would be that of one having a much smaller diameter. That's how most cameras work . . . f-stops, anyone?

Strictly speaking, the usual use of the word "aperture" in astronomy actually means

It's not the equivalent of a 130-meter diameter mirror; it's the equivalent of that mirror with all but four 8.2-meter diameter pieces of it blacked out. Yes, you can get a sharper image using interferometry, but your total light-gathering area is 211 square meters, not 13,273 square meters. That's going to affect exposure times. But still, it's cool.:)

Just what one needs to image the black hole at the center of the Milky Way. If they can get the timing right, between this set of 4 telescopes operating as one, the Keck telescopes in Hawaii, and the Spitzer IR Space Telescope, we could have a virtual telescope in the IR band that is easily 30,000 km wide.http://www.keckobservatory.org/ [keckobservatory.org] http://www.spitzer.caltech.edu/ [caltech.edu]

Btw: This idea increased spatial resolution using very long baseline interferometry is why it would be worth a few billion dollars to sen

The study of this proposed mission ended in 2007 with no further activities planned.

Ever since I heard about interferometry I thought we should put some satellites at far distant points (perhaps Earth's L2 and L3 points, with a repeater at L4 or L5 so the signal can get around the sun) and get some really impressive pictures of distant objects.

And X-ray telescopes in orbit (the Chandra X-Ray Observatory) and gamma ray telescopes in orbit (the Fermi Gamma-Ray Space Telescope) and on the ground (the MAGIC-I and II atmospheric imaging Cherenkov telescopes).

No, because no matter how high resolution the pics are, it will never be enough to satisfy the moon hoax morons.

I suggest that we round up the hoaxers, and in an attempt to prove to them that we really did land on the Moon in 1969, send them to Tranquility base, let them out, and remove their helmets, because the visors would distort the view.

And with their dying breaths, you would see them mouth the words "movie set."

Actually, I think(?) that a giant scope like these could never look at the Moon (and maybe Venus, the next brightest object in the night sky) is because the light gathering capability would burn the sensors.

I mean the light amplification from something 8m across down to about a centimeter(?) must be close to a million fold. So imagine moonlight a million times brighter. Gives new meaning to the expression "blinded me with science".

But maybe they put a piece of cardboard in front of the mirror and punch a

I heard on NPR the other day a story about Roger Angel, U. Arizona mirror guru, who's making 27-footers for installation in Chile by, I think it was, 2020. The amazing part is casting to that accuracy -- without exact uniformity. These 27-foot mirrors have to focus slightly off-center. Here's the transcript:
http://m.npr.org/news/Science/145837380 [npr.org]

No. Paranal is 24 d 37'; they should see down to 65d 23', but adding a few degrees for atmosphere and the pointing of the telescopes, they can see any part of the sky from 90 S to roughly 60 N, which is 87% of the whole sky.

I understand that (one of) the designs for the TPF was for four optically linked telescopes spanning about(?) 100m that using interferometry/optical nulling/coronagraphs could isolate enough light from a planet to get its spectrograph and thus determine if it (might) have life.

Of course the TPF was not only supposed to be in space but in DEEP space (in Jupiter orbit, at the trojan point?) so as to avoid the zodiacal light but is this overcome by the MUCH greater light capturing ab

Why not get a couple thousand 10" reflecting telescopes on digital servo mounts (~$1,500 each), hook them up to HD web cams (~$1,500 each), and use netbooks (~$300 each) with unlimited data plans (~$500/yr) to connect to database that uses a volunteer-based distributed computing network to process the data using inteferometry? You'd effectively have a telescope with a mirror the size of the Earth for about the cost of a professional level telescope. It would be orders of magnitude more powerful than anythin